One example of this kind of device is described in Japanese Patent Laid-Open No. 2012-197886. In this device, a rolling mass is oscillated by torque pulses of a rotary member, and the vibrations of the rotary member are suppressed by an oscillating motion of the rolling mass. The device taught by Patent Laid-Open No. 2012-197886 is used in a torque converter. In order to protect the rolling mass and a raceway surface from oil, the rolling mass is held in a chamber closed liquid-tightly by a damper housing.
In order to ensure the oscillating motion of the rolling mass, the rolling mass is arranged in such a manner as not to be contacted to the damper housing. However, a hydraulic pressure in the torque converter is raised when the torque converter is rotated at a high speed. In addition, the hydraulic pressure in the torque converter is also raised when applying a lockup clutch. If the hydraulic pressure in the torque converter is raised excessively, the damper housing may be deformed and the rolling mass may be brought into contact to an inner face of the damper housing. Consequently, the rolling mass will not be allowed to oscillate freely and hence vibration damping performance becomes poor. In addition, the rolling mass and the damper housing may be worn and damaged.